Diagnosis of influenza A virus infections by detection of specific immunoglobulins M, A, and G in serum.

The value of immunoglobulin M (IgM) detection in the early diagnosis of influenza A was examined in a prospective study during an outbreak of influenza A/Philippines/2/82 (H3N2) virus infection in February and March 1986. The IgM response was investigated in sera from 64 adults with influenzalike symptoms; we found a fourfold rise in titer or high titers (greater than or equal to 80) of influenza A virus antibodies by the complement fixation test. The IgM response, analyzed by the hemadsorption immunosorbent technique, was compared with the IgG and IgA responses analyzed by an indirect enzyme-linked immunosorbent assay and the hemadsorption immunosorbent technique, respectively. Antigen detection in nasopharyngeal secretions by immunofluorescence was performed for all patients on admission to hospital. Specific IgM was detected in 86% (55 of 64) of the patients with influenza A. In sera from 36% (18 of 64) of the patients it was detected already on admission. Influenza A virus antigen was detected in nasopharyngeal cells by immunofluorescence on admission in 53% (34 of 64) of the patients. A combination of immunofluorescence and IgM results gave a significantly higher diagnostic rate, 69% (P less than 0.01), on admission than did each of the two tests separately. An IgA serum antibody response was seen in 76% (48 of 64) of the cases but did not contribute to any increase in the diagnostic rate. IgM detection by the hemadsorption immunosorbent technique was found to be a valuable supplement for the diagnosis of influenza A in an early phase of the disease.